UV-C/UVGI – has been successfully tested in laboratories as a way to decontaminate N95 masks exposed to MS2 bacteriophage and influenza virus.


In recent weeks our distribution network in the healthcare sector is working non-stop. Our partners are professionals and experts in Infection Control, and they provided us with numerous application ideas, which can – or indeed, must – be shared as much as possible.

Lights4Health, our partner in the Netherlands, has just provided the SEH department (First Aid) at Leiden University Medical Center  with UV treatment cabinets. The systems will disinfect N65 masks in use by medical and paramedical staff.

Two studies on the UV-C treatment of the masks were published in leading scientific journals in 2015 and 2018, respectively, well before the recent release of Covid-19.

The problem of finding masks is a constant in the analysis of possible “apocalyptic” scenarios regarding the management of a global pandemic. One of the texts reports:


“The possibility of a global pandemic of an infectious respiratory disease is of tremendous concern to the occupational health community because healthcare workers would face the greatest risk of exposure.

For pandemic diseases that may be transmitted by airborne particles, the isolation precaution guidelines from the Centers for Disease Control and Prevention (CDC) call for healthcare workers to wear respiratory protection while treating patients. Because of their loose fit and low filtration capacity, surgical masks do not provide respiratory protection from small airborne particles.

For this reason, the most common respiratory protection device used in healthcare settings is the disposable N95 filtering face-piece respirator (FFR). However, infection control procedures typically call for disposable FFRs to be discarded after a single use to avoid cross-contamination.

This means that a pandemic of a disease such as influenza would require a tremendous number of FFRs to protect healthcare workers from the airborne transmission. The Institute of Medicine (IOM) projected that a 6-week influenza pandemic would require 90 million FFRs. The Occupational Safety and Health Administration (OSHA) has predicted that an influenza pandemic would likely last 24 weeks, which suggests that up to 360 million FFRs could be needed in the United States alone.

A surge in demand of this magnitude would greatly exceed current stockpiles and production capabilities, and would almost certainly result in a shortage.”

One way to meet the growing need for masks during a pandemic would be to reuse them, as even a small number of reuses of each mask would greatly expand the available stock of disposable respirators. During the 2009 H1N1 pandemic, the CDC (“Centers for Disease Control and Prevention” USA) recommended that healthcare facilities consider extending the use and reuse of N95 respirators in cases of extreme need. Buying masks in bulk quantities represents a significant cost, in addition to the difficulties associated with production and distribution processes.

However, a significant concern for reuse is the possibility that the external surfaces of the respirator may become contaminated with infectious material and lead to disease transmission. To avoid this risk, masks should be decontaminated after each use.

Several techniques have been tested for the decontamination of N95 FFR. These include autoclaves, steam generated by heat or microwaves, ethylene oxide, vaporized hydrogen peroxide, and bleach. All the methods described have advantages and disadvantages. Heat and steam, for example, may dissolve or degrade the respirator and require the device to dry after treatment.

Chemical disinfectants require rinsing and drying and may leave an unpleasant odor or residue that irritates the skin. Gaseous systems using ethylene oxide or vaporized hydrogen peroxide require specialized equipment and ventilation controls.


N95 systems cannot be disinfected with alcohols such as isopropanol, because the alcohols remove the electrostatic charge from the filtration medium and substantially degrade its filtration capacity.

An important consideration for all decontamination methods, including UVGI, is the risk that they degrade the respirator material and reduce the ability of the mask to filter out infectious bioaerosols.

Some studies have examined the effects of UVGI on the respirator’s appearance, fit, airflow resistance, and filtration efficiency after one or three decontamination cycles and found no significant effects. However, the effects of prolonged UVGI exposure after multiple decontamination cycles are not known and it is unclear how much a cumulative dose of UVGI respirators can withstand, what damage will occur at the end or how many times disposable masks can potentially be decontaminated and reused.

This suggests that the upper limit for UVGI exposure during repeated disinfection cycles should be set by physical degradation of the respirator material and not by loss of filtration capacity. For some FFRs models, this could potentially be used as a useful warning: if the respirator material is significantly degraded after UVGI disinfection, the mask should obviously be discarded.

It is advisable – for even more effective action – to subject the mask to dry heating at around 60°C to inactivate potential infectious nuclei trapped within the filter weave as much as possible.

Of course, it would be desirable to have sufficient time and possibilities to quickly design N95 masks specifically for healthcare professionals that can be disinfected even 50 times with UV-C disinfection cycles in less than 60 seconds, however, the current situation makes this operation impractical.

Lindsley WG, Martin SB Jr, Thewlis RE, et al. Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity. J Occup Environ Hyg. 2015;12(8):509–517. doi:10.1080/15459624.2015.1018518
Ultraviolet germicidal irradiation of influenza-contaminated N95 filtering facepiece respirators” Mills, Devin et al. American Journal of Infection Control, Volume 46, Issue 7, e49 – e55
Kowalski, Wladyslaw. (2020). 2020 COVID-19 Coronavirus Ultraviolet Susceptibility. 10.13140/RG.2.2.22803.22566.
Hang L, Yang Y-R, Zhang Z, Lin Z. (2020). Genomic variations of COVID-19 suggest multiple outbreak sources of transmission. medRIX (preprint).
20. Zhu N, Zhang D, Wang W, Li X, Yang B, Song J, Zhao X, Huang B, Shi W, Lu R and others. (2020). “A Novel Coronavirus from Patients with Pneumonia in China”, 2019. N Engl J Med 382,727-733.
Hang L, Yang Y-R, Zhang Z, Lin Z. (2020). “Genomic variations of COVID-19 suggest multiple outbreak sources of transmission.” medRIX (preprint).